1. Field of the Invention
The present invention relates to a communication apparatus such as a serial communication apparatus or the like which communicates with one or plural communication devices on a communication line.
2. Related Background Art
FIG. 11 shows an structural example of a conventional serial communication system. In this system, a communication controller 101, a communication IC 102 to which a motor driver 105 for driving a motor 104 is connected, and a communication IC 103 to which plural sensors 106 are connected are cascade-connected through a set of signal lines consisting of a total of four lines, i.e., a +5V line acting as a power supply line, a ground (GND) line, a sync clock (CLK) line for serial communication and a data (DATA) line.
The eight communication IC""s can be maximally cascade-connected to one communication controller 101, and an inherent address (address 0, address 1, . . . ) can be designated to each communication IC. In FIG. 11, the two communication IC""s 102 and 103 are cascade-connected to the controller 101. On the other hand, eight data registers 0 to 7 are provided inside the controller 101. These registers 0 to 7 are respectively corresponding to the inherent addresses (addresses 0 to 7) of the communication IC""s, and each register is selected by a serial communication control unit 120.
Such the communication controller 101 as above communicates, i.e., transmission or reception, with the communication IC corresponding to each of the data registers. At a transmission time, data is transmitted from the controller 101 through a transmission buffer 121 and a shift register 122. On the other hand, at a reception time, data is received from the communication IC through a shift register 124 and a reception buffer 123.
FIG. 12 shows a structural example in a case where the above-described serial communication system is used inside an image formation apparatus 1 such as a copy machine or the like.
In FIG. 12, a host CPU (not shown) and a communication controller 201 are bus-connected to each other by means of an address bus, a data bus and a control signal bus. Further, the communication controller 201, a communication IC 202 to which a motor driver 208 for driving a motor 206 positioned at an appropriate location inside the apparatus is connected, a communication IC 203 to which a motor driver 209 for driving a motor 207, a communication IC 204 to which plural sensors 210 are connected, and a communication IC 205 to which plural sensors 211 are connected are connected through a set of signal lines. Thus, data communication between the communication controller 201 and each of the communication IC""s 202 to 205 is performed in response to a transmission instruction or a reception instruction issued from the host CPU.
Irrespective of locations of these communication IC""s 202 to 205 in the apparatus, an inherent address (address 0, address 1, address 2, . . . ) is determined for each communication IC. Thus, by designating the address in a communication frame (pulse column), the communication controller 201 performs the transmission/reception to/from the communication IC of which address corresponds to the designated address.
Subsequently, the outline of an operation of the above-described serial communication system will be explained hereinafter. In case of performing a transmission operation for transmitting a predetermined-phase data to drive or rotate the motor 206, the host CPU stands a transmission flag for performing the transmission in the communication controller 201 and writes transmission data into the data register 0. When the transmission data is written, the controller 201 sends a predetermined-frequency pulse column to a CLK line.
By using such a system structure, it becomes possible to operate a number of motors and sensors positioned at various locations in the apparatus by using the four cascade-connected signal lines and read the information from the signal lines. In this conventional serial communication system, one address is represented by eight bits, and the information of the eight addresses is managed between the communication controller and the communication IC""s. However, according to an agreement of a communication data format, such the structure of the conventional system can be modified to an adequately optimized structure. In addition, by setting plural communication controller functions and thus increasing the number of the signal lines corresponding to the plural functions, the number of the communication IC""s can be increased.
Generally, in a case where the number of the communication IC""s connected to a set of communication lines is small, if the communication IC""s are connected respectively to the separate communication lines, i.e., a multi-system connection state is set, and then the serial communication is performed, processing efficiency may be improved rather than the cascade-connected structure.
For example, for the communication IC connected to a load of which delay is not permitted or a load of which speed is low, it is better to select the address of which communication priority order is as higher as possible. For this reason, in the case where the number of the communication IC""s is small, it is better to set the multi-system connection state as numerous as possible and then perform the serial communication.
On the contrary, the communication IC connected to a load of which delay is permitted to some extent is not so affected by the communication priority order. Therefore, in a case where the number of such the communication IC""s is large, also in consideration of system assembly or the like, it is more effective to connect all the communication IC""s to one set of the communication lines and then perform the serial communication.
However, in the above-described conventional serial communication system, the number of the communication lines can not arbitrarily changed according to the number of the communication IC""s, load conditions of the motor, the sensor and the like connected to the communication IC""s, and the like. As a result, there has been a problem that the serial communication can not be effectively performed.
For example, as shown in FIG. 11, in the case where merely the two communication IC""s 102 and 103 are used in one unit although the eight communication IC""s can be maximumly cascade-connected to one set of the communication lines, efficiency in the serial communication becomes seriously degraded, it depends on the load conditions, though.
Therefore, an object of the present invention is to provide a data transfer system which can effectively perform, according to the number of communication IC""s connected to communication lines and load conditions connected to the communication IC""s, serial communication by dividing the communication lines into one or plural systems and using the divided-system communication lines.